Herlinde Koelbl: photos of Angela Merkel over the years.
There is also Pantone Merkel by Noortje van Eekelen:
See also Andreas Gursky’s painting of the four chancellors.
LATER NOTE: An article in The Guardian showing some of the Herlinde Koelbl photos.
EVEN LATER NOTE: There is also an Instagram account called merkellooks, collecting all kinds of images of Merkel.